A device and method for treating side stream sludge with formate to achieve short-range nitrification

Abstract

A device and method for treating sidestream sludge with formate to achieve short-cut nitrification belongs to the field of urban sewage treatment and regeneration. The metabolic diversity of nitrite-oxidizing bacteria (NOB) is utilized to perform sidestream treatment with VFAs such as formate to achieve mainstream short-cut nitrification. The sludge is returned from the bottom of the secondary sedimentation tank to the anaerobic zone and the dosing regulating tank respectively. Formate is added to the dosing regulating tank. The PLC controller controls the COD concentration at 140-160 mg / L. The returned sludge is mixed in the dosing regulating tank and enters the front end of the aerobic zone. The reflux ratio R2 = 100%; when the nitrite accumulation rate (NAR) is higher than 60%, R2 is adjusted to 50%; when the NAR is higher than 80%, R2 is adjusted to 25%. The present invention achieves short-cut nitrification with little impact on ammonia oxidizing bacteria (AOB), does not affect the total nitrogen removal rate, and achieves sludge reduction and resource utilization; as the NAR increases, the amount of formate added is gradually reduced, and short-cut nitrification is maintained while reducing formate consumption, saving costs.

Description

Technical Field

[0001] The invention belongs to the field of urban sewage treatment and regeneration, and particularly relates to a device and method for treating side stream sludge with formate to achieve short-range nitrification. Background Art

[0002] With the accelerating pace of urbanization, urban wastewater treatment has become a critical issue in urban environmental protection and water resource management. Nitrogen pollution is a significant concern in urban wastewater treatment. Nitrogen pollution can lead to eutrophication, posing a threat to aquatic ecosystems and human health. Therefore, deep denitrification of nitrogen in urban wastewater is crucial. Deep denitrification involves reducing nitrogen pollutants in urban wastewater to extremely low levels, typically performed at the final stage of the wastewater treatment system. Traditional deep denitrification methods include biological, chemical, and physical methods. Biological methods are currently the most commonly used, including biofilm processes, aerobic / anaerobic denitrification, and simultaneous nitrification and denitrification. These methods utilize the metabolic activity of microorganisms to convert nitrogen pollutants into nitrogen gas emissions. In addition to deep denitrification, energy conservation and consumption reduction are also crucial issues in urban wastewater treatment. Urban wastewater treatment is an energy-intensive process, with major energy consumption coming from intake pumping stations, aeration equipment, mixing equipment, compressed air systems, and sludge handling. Therefore, reducing energy consumption in urban wastewater treatment is a hot topic of research. Some energy-saving and consumption-reducing technologies include adopting low-energy-consuming equipment, optimizing sewage treatment processes, and recycling and utilizing energy. Therefore, the research and application of deep denitrification and energy-saving and consumption-reducing technologies for urban sewage are of great significance to urban environmental protection and water resources management.

[0003] The biological denitrification process includes aerobic nitrification and subsequent anoxic denitrification, in which nitrification is carried out by ammonia oxidizing bacteria (AOB) to convert NH4 + Oxidized to NO2 - , and then nitrite oxidizing bacteria (Nitrite Oxidizing Bacteria, NOB) converts NO2 - Oxidized to NO3 - Denitrification is the process by which denitrifying bacteria convert NO3 - Reduction to NO2 - , NO2 - Then it is gradually reduced to N2, thus completing the liquid phase NH4 +Converted into N2 in the gas phase to achieve denitrification. According to the nitrification and denitrification processes, on the one hand, aerobic nitrification requires aeration energy consumption. According to reports, the aeration energy consumption required for nitrification accounts for 60% of the total energy consumption of a sewage treatment plant. On the other hand, denitrification requires the consumption of organic matter, and the actual organic matter in sewage is often relatively scarce. It is a low carbon / nitrogen ratio (C / N, also known as COD / TIN, COD: Chemical Oxygen Demand, TIN: Total Inorganic Nitrogen) sewage, which requires additional carbon source. But if nitrification can be controlled within NO2 - stage, and do not allow it to continue to oxidize into NO3 - , which will be able to save NO2 - to NO3 - and NO3 - to NO2 - These two steps can save 25% of aeration energy consumption and 40% of denitrification carbon source, which is an energy-saving and cost-reducing denitrification method. - The stage is not further oxidized to NO3 - , is the concept of short-range nitrification. Based on short-range nitrification, anaerobic ammonium oxidation (Anammox) is a new type of sewage treatment technology, which uses the metabolic process of specific microorganisms under anaerobic conditions to convert NH4 + and NO2 - At the same time, it is converted into nitrogen. This technology has the advantages of high efficiency, low energy consumption, and no need for external carbon source. It is widely used in urban sewage treatment, agricultural wastewater treatment, industrial wastewater treatment and other fields. To carry out the anammox reaction, NH4 is needed + and NO2 - As substrate, NH4 + -N can be obtained directly from sewage, while NO2 - The source of NO2 is the key. - The combination of short-range nitrification and anaerobic ammonium oxidation has thus come into being, which is called short-range nitrification-anaerobic ammonium oxidation technology. This patent provides a method for the rapid implementation of a short-range nitrification system, and facilitates the short-range nitrification-anaerobic ammonium oxidation technology.

[0004] Recent research indicates that NOB in ammonia oxidation can utilize formic acid or acetic acid from volatile fatty acids (VFAs) as active ingredients for growth, thereby replacing the nitrite oxidation process. Compared to simply adding inhibitors (such as FA, FNA, formic acid, and chloride), altering NOB metabolic pathways can avoid the short-term nitrification disruption caused by NOB adaptability to inhibitors, resulting in a more stable and rapid short-term nitrification process.

[0005] This patent proposes a method for achieving PN in sidestream sludge by treating it with formate, which avoids the short-range nitrification damage caused by traditional inhibitors. Specifically, by setting up a dosing regulating tank, 150mgCOD / L of sodium formate is added to the dosing regulating tank to treat secondary sedimentation tank sludge, achieving NOB suppression and providing a feasible method for achieving PN in the mainstream. Summary of the Invention

[0006] The present invention aims to provide a device and method for deep denitrification of low-C / N ratio municipal sewage by treating sidestream sludge with formate to achieve short-cut nitrification. In this device, domestic sewage from a sewage source tank enters the anaerobic zone of a biochemical tank, along with activated sludge returning from a secondary sedimentation tank. Under anaerobic conditions, phosphorus-accumulating bacteria release phosphorus, converting COD and VFAs to PHA, and ammonifying some nitrogen-containing organic matter. The sewage then enters the anoxic zone. Nitrite nitrogen produced by short-cut nitrification in the aerobic zone is returned to the anoxic zone via digestion fluid. Some organic matter is degraded and removed by denitrifying bacteria using nitrite as an electron acceptor. The mixed liquor then enters the aerobic zone, where ammonia nitrogen nitrification and phosphorus absorption occur. Using formate as a carbon source, short-cut nitrification is achieved, converting ammonia nitrogen to nitrite nitrogen, and excess phosphorus absorbed in the sludge is discharged as residual sludge.

[0007] A device and method for treating side stream sludge with formate to achieve short-cut nitrification, characterized by:

[0008] 1) System startup phase:

[0009] Short-cut nitrification was achieved in a biochemical tank inoculated with fully nitrifying and denitrifying sludge. The volume ratio of the anaerobic, anoxic, and aerobic zones in the biochemical tank was 1:3:4. The sludge return ratio (R1) from the sedimentation tank to the front end of the anaerobic zone was 100%, and the sludge return ratio (R2) from the dosing regulating tank to the front end of the aerobic zone was 100%. Formate was added to the dosing regulating tank to an initial concentration of 150 mgCOD / L, and the dosage was subsequently controlled by a PLC control system to maintain the formate concentration at 140-160 mgCOD / L. The hydraulic retention time (HRT) in the biochemical tank was 16 hours, and that in the dosing regulating tank was 2.67 hours. The sludge concentration in the system was controlled at 3000±500 mg / L. The dissolved oxygen in the aerobic zone was controlled at 1.0-2.5 mg / L. The system startup phase was considered complete when the nitrite accumulation rate (NAR) reached above 60% and was maintained stably for more than 20 days.

[0010] 2) Stable operation stage:

[0011] During the stable operation phase, the sludge concentration in the system is controlled at 3000±500mg / L; the dissolved oxygen in the aerobic zone is controlled at 1.0-2.5mg / L. When the NAR exceeds 60%, the PLC control system controls the return flow ratio (R2) from the dosing regulating tank to the aerobic zone front end to 50%, and the hydraulic retention time (HRT) of the dosing regulating tank is 4.44h. When the NAR exceeds 80%, the return flow ratio (R2) from the dosing regulating tank to the aerobic zone front end is adjusted to 25%, and the HRT of the dosing regulating tank is 8h. During the stable operation phase, the PLC control system maintains the COD concentration in the dosing regulating tank at 140-160mg / L. This method has a maximum HRT of 8h, which is different from sludge fermentation.

[0012] 3) The PLC controller calculates the formate addition flow rate q value based on the X and Y values of the CODcr online monitoring equipment, and adjusts the q value through the dosing pump and electromagnetic valve to achieve a constant COD concentration in the regulating tank at 140-160 mg / L.

[0013]

[0014] in:

[0015] q: Formate flow rate; controlled by the pump and adjusted once every t time, (L / min);

[0016] R: Real-time reflux rate: R is 100%, 50% or 25%;

[0017] Q: water inlet flow rate, (L / min);

[0018] t: Adjustment frequency; (10min);

[0019] X: effluent COD concentration; online monitor reading, (mg / L);

[0020] Y: COD concentration in the dosing regulating tank; online monitor reading, (mg / L);

[0021] V: volume of dosing tank, m 3

[0022] The method of the present invention for rapidly starting short-range nitrification by adding formate in a continuous flow has the following advantages over the prior art:

[0023] (1) The use of side stream treatment technology can effectively reduce the impact of organic matter on AOB in sewage treatment systems, thereby improving the removal efficiency of ammonia nitrogen.

[0024] (2) The side stream of the residual sludge is treated, and the VFA produced by in-situ sludge hydrolysis and acidification and the additional addition of formate are used to jointly inhibit the nitrite oxidation pathway of NOB, which is conducive to the reduction of sludge and resource utilization, and has good economic and practical feasibility.

[0025] (3) The additional carbon source introduced through side stream treatment can increase the activity of ammonia oxidizing bacteria and denitrifying bacteria in the system, achieving deep denitrification while achieving PN. By utilizing the carbon source, the bacteria in the sludge can also obtain better growth conditions, making the sludge treatment efficiency higher. Therefore, the side stream treatment method of introducing an additional carbon source has broad application prospects and has a positive effect on improving sewage treatment efficiency and reducing environmental pollution.

[0026] (4) After PN is realized, it is expected to be combined with anaerobic ammonium oxidation to achieve energy saving and consumption reduction for deep pollutant removal. The combination of PN technology and anaerobic ammonium oxidation technology is an innovative wastewater treatment technology that can achieve more efficient, economical and sustainable wastewater treatment, and is expected to become an important development direction in the future wastewater treatment field.

[0027] (5) The addition of inhibitors often has an adverse effect on the denitrification effect of the system. However, the addition of formate as a carbon source can improve the denitrification effect of the system while inhibiting the activity of NOB, achieving short-term nitrification, and is expected to be applied in actual sewage treatment plants. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of the structure of the device for treating side stream sludge with formate to achieve short-cut nitrification.

[0029] 1 is the sewage raw water tank, 2 is the biochemical pool, 3 is the sedimentation tank, 4 is the dosing adjustment tank, 5 is the dosing tank, 6 is the PLC controller, 7 is the computer, 1.1 is the sewage raw water tank overflow pipe, 1.2 is the sewage raw water tank vent pipe, 1.3 is the sewage raw water tank outlet pipe, 1.4 is the water inlet pump, 2.1 is the biochemical pool inlet pipe, 2.2 is the agitator, 2.3 is the DO detector, 2.4 is the air compressor, 2.5 is the gas flow meter, 2.6 is the aeration plate , 2.7 is the digestate return pump, 3.1 is the sludge return pump, 3.2 is the overflow weir, 4.1 is the agitator of the dosing regulating tank, 4.2 is the pH detector, 4.3 is the sludge return pump of the dosing regulating tank, 6.1 is the dosing pump, 6.2 is the sludge return electromagnetic valve to the aerobic zone, 6.3 is the sludge return electromagnetic valve to the dosing regulating tank, 6.4 is the CODcr online monitoring equipment of the dosing regulating tank, and 6.5 is the CODcr online monitoring equipment of the sedimentation tank.

[0030] Figure 2 These are the test results from a test using sodium formate. DETAILED DESCRIPTION

[0031] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0032] A device for treating side stream sludge with formate to achieve short-range nitrification is provided, comprising a sewage raw water tank (1), a biochemical tank (2), a sedimentation tank (3), a dosing and regulating tank (4), a dosing tank (5), a PLC controller (6), and a computer (7); the sewage raw water tank (1) is provided with an overflow pipe (1.1), a vent pipe (1.2), and a water outlet pipe (1.3); the sewage raw water tank is connected to the water inlet (2.1) of the biochemical tank (2) via an inlet pump (1.4); the biochemical tank (2) is divided into three zones, namely, an anaerobic zone, an anoxic zone, and an aerobic zone, along the water inlet direction; each cell is provided with a stirrer (2.2), and the aerobic zone is provided with an aeration device and a DO detector (2.3), the aeration device consists of an air compressor (2.4), a gas flow meter (2.5) and an aeration plate (2.6); the aerobic zone is used to return the digestate through a digestate return pump (2.7), the effluent from the aerobic zone enters the sedimentation tank (3), the bottom sludge is returned to the front end of the anaerobic zone and the dosing regulating tank (4) through a sludge return pump (3.1), and the upper clear water is discharged through an overflow weir (3.2); the dosing regulating tank (4) is equipped with a stirrer (4.1) and a pH detector (4.2), and the sludge fermentation mixture is added to the front end of the aerobic zone through a sludge return pump (4.3); the dosing tank (5) contains formate with an effective ingredient of 150gCOD / L.

[0033] The PLC control system includes a PLC controller (6), a computer (7), a dosing pump (6.1), a solenoid valve for sludge return to the aerobic zone (6.2), a solenoid valve for sludge return to the dosing regulating tank (6.3), a CODcr online monitoring device for the dosing regulating tank (6.4), and a CODcr online monitoring device for the sedimentation tank (6.5), and the above instruments and equipment are all connected through communication.

[0034] The septic tank wastewater from a family compound of a university in Beijing was treated. The specific water quality during operation was as follows: COD was 100-200 mg / L, NH4 + -N is 30-80mg / L, NO3 - -N≤2mg / L, NO2 - -N≤0.5mg / L. Test system such as Figure 1 shown.

[0035] The specific operations are as follows:

[0036] 1) System startup phase:

[0037] Short-cut nitrification was achieved in a biochemical tank inoculated with fully nitrifying and denitrifying sludge. The volume ratio of the anaerobic, anoxic, and aerobic zones in the biochemical tank was 1:3:4. The sludge return ratio (R1) from the sedimentation tank to the front end of the anaerobic zone was 100%, and the sludge return ratio (R2) from the dosing regulating tank to the front end of the aerobic zone was 100%. Formate was added to the dosing regulating tank to an initial concentration of 150 mgCOD / L, and the dosage was subsequently controlled by a PLC control system to maintain the formate concentration at 140-160 mgCOD / L. The hydraulic retention time (HRT) in the biochemical tank was 16 hours, and that in the dosing regulating tank was 2.67 hours. The sludge concentration in the system was controlled at 3000±500 mg / L. The dissolved oxygen in the aerobic zone was controlled at 1.0-2.5 mg / L. The system startup phase was considered complete when the nitrite accumulation rate (NAR) reached above 60% and was maintained stably for more than 20 days.

[0038] 2) Stable operation stage:

[0039] During the stable operation phase, the system's sludge concentration is controlled at 3000±500mg / L; the dissolved oxygen in the aerobic zone is maintained at 1.0-2.5mg / L. When the NAR exceeds 60%, the PLC control system maintains the recirculation ratio (R2) from the dosing regulating tank to the aerobic zone at 50%, with a hydraulic retention time (HRT) of 4.44h. When the NAR exceeds 80%, the recirculation ratio (R2) from the dosing regulating tank to the aerobic zone is adjusted to 25%, with a HRT of 8h. During the stable operation phase, the PLC control system maintains the COD concentration in the dosing regulating tank at 140-160mg / L. Initial VFA production in the system is provided by formate. As the recirculation ratio (R2) decreases, sludge ferments in the dosing regulating tank to produce VFA, and the formate dosage, regulated by the PLC controller, is gradually reduced, saving costs without affecting short-range nitrification.

[0040] 3) The PLC controller calculates the formate addition flow rate q value based on the X and Y values of the CODcr online monitoring equipment, and adjusts the q value through the dosing pump and electromagnetic valve to achieve a constant COD concentration in the regulating tank at 140-160 mg / L.

[0041]

[0042] in:

[0043] q: Formate flow rate; controlled by the pump and adjusted once every t time, (L / min);

[0044] R: Real-time reflux rate: R is 100%, 50% or 25%;

[0045] Q: water inlet flow rate, (L / min);

[0046] t: Adjustment frequency; (10min);

[0047] X: effluent COD concentration; online monitor reading, (mg / L);

[0048] Y: COD concentration in the dosing regulating tank; online monitor reading, (mg / L);

[0049] V: volume of dosing tank, m 3

[0050] 4) Test results

[0051] like Figure 2 As shown, experiments using sodium formate showed that when the sodium formate concentration was below 100 mgCOD / L, the ammonia nitrogen degradation rate was equivalent to the nitrate nitrogen generation rate, and short-term nitrification was not achieved. When the sodium formate concentration reached 150 mgCOD / L, the nitrite oxidation rate was less than 0, indicating that the nitrite oxidation pathway was suppressed, which is conducive to PN. The study found that the formate addition concentration was negatively correlated with the nitrate nitrogen generation rate and positively correlated with the nitrite degradation rate, achieving both short-term nitrification and efficient nitrogen removal.

[0052] The above are specific embodiments of the present invention, which are convenient for those skilled in the art to better understand and apply the present invention. The implementation of the present invention is not limited to this, so simple improvements made to the present invention by those skilled in the art are within the scope of the present invention.

Claims

1. A method for treating side stream sludge with formate to achieve short-range nitrification, the device used in the method comprising a sewage raw water tank (1), a biochemical tank (2), a sedimentation tank (3), a dosing and regulating tank (4), a dosing tank (5), a PLC controller (6) and a computer (7); the sewage raw water tank (1) is provided with an overflow pipe (1.1), a vent pipe (1.2) and a water outlet pipe (1.3); the sewage raw water tank is connected to the water inlet (2.1) of the biochemical tank (2) by a water inlet pump (1.4); the biochemical tank (2) is divided into three areas, which are an anaerobic area, an anoxic area and an aerobic area in the direction of water inlet, each cell is provided with a stirrer A (2.2), the aerobic area is provided with an aeration device and a DO detector (2.3), and the aeration device is provided with a DO detector (2.3). The device is composed of an air compressor (2.4), a gas flow meter (2.5) and an aeration plate (2.6); the aerobic zone is refluxed with nitrification liquid through a nitrification liquid reflux pump (2.7), the effluent of the aerobic zone enters a sedimentation tank (3), the bottom sludge is refluxed to the front end of the anaerobic zone and the dosing regulating tank (4) through a sludge reflux pump A (3.1), and the upper clear water is discharged through an overflow weir (3.2); the dosing regulating tank (4) is provided with a stirrer B (4.1) and a pH detector (4.2), and the sludge fermentation mixture is added to the front end of the aerobic zone through a sludge reflux pump B (4.3); the dosing tank (5) contains formate with an effective ingredient of 150gCOD / L; the dosing tank (5) is connected to the dosing regulating tank (4); The PLC control system includes a PLC controller (6), a computer (7), a dosing pump (6.1), a solenoid valve for sludge return to the aerobic zone (6.2), a solenoid valve for sludge return to the dosing regulating tank (6.3), a CODcr online monitoring device for the dosing regulating tank (6.4), and a CODcr online monitoring device for the sedimentation tank (6.5), and the above instruments and equipment are all connected via communication; It is characterized by: The following steps are involved: 1) System startup phase: Short-cut nitrification was achieved in a biochemical tank inoculated with fully nitrified and denitrified sludge. The volume ratio of the anaerobic, anoxic, and aerobic zones in the biochemical tank was 1:3:

4. The sludge return ratio (R1) from the sedimentation tank to the front end of the anaerobic zone was 100%, and the sludge fermentation mixture from the dosing regulating tank to the front end of the aerobic zone was 100%. Formate was added to the dosing regulating tank to an initial concentration of 150 mgCOD / L, and the dosage was subsequently controlled by a PLC control system to maintain the COD concentration between 140 and 160 mg / L. The hydraulic retention time (HRT) in the biochemical tank was 16 hours, and that in the dosing regulating tank was 2.67 hours. The sludge concentration in the system was controlled at 3000 ± 500 mg / L. The dissolved oxygen in the aerobic zone was controlled at 1.0-2.5 mg / L. The system startup phase was considered complete when the nitrite accumulation rate (NAR) reached above 60% and remained stable for more than 20 days. 2) Stable operation stage: During the stable operation phase, the sludge concentration in the system is controlled at 3000±500mg / L; the dissolved oxygen in the aerobic zone is controlled at 1.0-2.5mg / L; when the NAR is higher than 60%, the PLC control system controls the return flow ratio R2 from the dosing regulating tank to the front end of the aerobic zone to 50%, and the hydraulic retention time of the dosing regulating tank is 4.44h; when the NAR is higher than 80%, the return flow ratio R2 from the dosing regulating tank to the front end of the aerobic zone is adjusted to 25%, and the hydraulic retention time of the dosing regulating tank is 8h; During the stable operation stage, the COD concentration in the dosing regulating tank is maintained at 140-160 mg / L through the PLC control system.

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